The coronavirus is an etiological agent of affects both animals and humans. Sever acute respiratory syndrome (SARS-2) and (SARS-1) are caused by two viruses belonging to subgenus beta-coronavirus. SARS-1 and SARS-2 are considered zoonotic diseases transmitted from animals to human causing epidemic SARS-1 and pandemic SARS-2. In animals and humans both viruses have a tropism binding receptors the ACE2 which is the entry site for host cells. In animal virus affected all aged and cause disturbances in all organs but main clinical signs are respiratory disorder with development some complications and organs failure functions in advance cases. Similarity of both SARS-1 and SARS-2 resulted in thrombus formation accompanied with elevated d-dimer, increase fibrin formation and long time for prothrombin. Inaddition neurological disorder and olfactory dysfunction was detected in SARS-2. This review focused on the coronavirus transmission, host defense mechanisms, pathophysiology and pathogenesis. There was similarity and different points between SARS-1 and SARS-2, but in general SARS2 is less pathogenic and more rapidly transmissible than SARS-1.